The invention is based on a pressure modulator for a hydraulic brake system, especially a motor vehicle brake system. A pressure modulator that is used to modulate the pressure of the pressure fluid in the wheel brake cylinders is already known from German Patent Disclosure DE 37 41 310 A1, U.S. Pat. No. 4,461,116. This pressure modulator has a first cylinder with a servo piston, a second cylinder with a control piston, and a guide bore which connects the first cylinder with the second cylinder and in which a control tappet is disposed. The control tappet is located in the first cylinder at one face end of the servo piston and in the second cylinder at one face end of the control piston. In the second cylinder, a shutoff valve is disposed offset from a longitudinal axis of the pressure modulator. In this kind of pressure modulator, exact guidance of the servo piston in the first cylinder is not always assured, because the imposition of pressure on the servo piston by the pressure fluid creates the danger of a skewed position and therefore of leakage from the pressure modulator. The production of the eccentrically disposed shutoff valve requires high production expense.